1. Field of the Invention:
The present invention relates to a process for preparing oxytitanium phthalocyanine. More particularly, it relates to a process for preparing a specific crystal form of oxytitanium phthalocyanine.
2. Description of the Prior Art:
Phthalocyanines are known compounds useful as colorants for paints, printing inks and resins, or as electronic materials. In particular, they have been utilized as photosensitive materials in electrophotography on an extensive scale.
The present inventors have studied processes for preparing oxytitanium phthalocyanine in great detail and found that oxytitanium phthalocyanine exists in three different crystal forms, hereinafter referred to as "A form", "B form" and "C form", respectively, depending upon subtle differences of conditions for preparing oxytitanium phthalocyanine.
FIGS. 1 to 3 show the powder X-ray diffraction patterns of said three crystal forms of oxytitanium phthalocyanine, respectively. Strong, characteristic diffraction peaks are seen at Bragg angles (2.theta.) of 9.3.degree. and 26.3.degree. for the A form (FIG. 1), at 7.6.degree. and 28.6.degree. for the B form (FIG. 2), and at 7.0.degree. and 15.6.degree. for the C form (FIG. 3).
Generally, oxytitanium phthalocyanne is obtained in the form of a mixture of the above said crystal forms. Such a mixture may readily cause difficulties due to the non-uniformity in physical properties of each of the crystal forms since they have different physical properties from one another.
Of course, it is generally desirable to prepare oxytitanium phthalocyanine in a pure crystal form.
In practice, oxytitanium phthalocyanine is often dispersed in various polymers or solvents, applied on base materials such as polyester films and dried so as to manufacture commercially available articles. However, since the interaction between oxytitanium phthalocyanine and various polymers or solvents varies with different crystal forms, the use of mixtures of two or more crystal forms of oxytitanium phthalocyanine often interferes with the dispersibility of the crystals in polymers or solvents resulting in a failure in obtaining predicted physical properties.
Thus, the development of a process for preparing a pure crystal form of oxytitanium phthalocyanine is eagerly desired in order to eliminate such defects as encountered by the prior art.
Among three aforementioned crystal forms of oxytitanium phthalocyanine, the A form is especially useful as a photo-conductive material in electrophotography.
The present inventors have made great efforts to obtain the pure A form crystal of oxytitanium phthalocyanine and finally found that under certain specific conditions, only the A form of oxytitanium phthalocyanine can selectively be produced. Thus, the present inventors have now attained this invention.